Authors: Silja Räty, MD, PhD
Department of Neurology, Helsinki University Hospital, Finland
The posterior circulation is affected in the minority of ischaemic strokes, with symptoms ranging from isolated homonymous hemianopia in distal posterior cerebral artery occlusions (PCAo) to coma or locked-in syndrome in the most severe forms of basilar artery occlusion (BAo). Compared to anterior circulation infarcts, posterior circulation strokes are less well recognised in the acute phase, receive less reperfusion therapy, and have longer treatment delays (1,2,3).
Endovascular thrombectomy (EVT) is the standard treatment for anterior circulation large vessel occlusion (4), but similar evidence for posterior circulation stroke has been lacking until recently. Due to its clinical severity, BAo has been a target for reperfusion treatments for decades, but the first large randomised controlled trials on the topic came out only in 2020‒2021, when the BEST and BASICS trials reported neutral results of EVT + best medical treatment (BMT) versus BMT alone (5,6). They were followed by the recently published ATTENTION and BAOCHE trials that were first to demonstrate better functional outcome, as well as lower mortality in the former trial, for patients with BAo receiving EVT + BMT compared to BMT up to 24 hours from symptom onset (7,8). In both trials, 46% of patients in the EVT + BMT group achieved a 3-month modified Rankin Scale score of 0‒3 in comparison to 23 to 24% in the BMT group (adjusted rate ratios 2.06 [95% CI 1.46−2.91] and 1.81 [95% CI 1.26−2.60]). The frequency of symptomatic intracranial haemorrhage did not differ between the treatment arms.
However, the trial results have left some questions unanswered. First, intravenous thrombolysis (IVT) was received by only 14‒34% of the trial populations in ATTENTION and BAOCHE, so it remains uncertain whether EVT is superior to IVT alone. Moreover, the subgroup analysis of patients treated with IVT could not show benefit of additional EVT (7). Second, the positive trials have included mostly patients with moderate to severe symptoms, so the optimal approach to patients with milder clinical presentation is less clear. Finally, intracranial atherosclerosis is remarkably frequent aetiology of BAo in Asia, which hampers applicability of the trial results to European populations.
Lately, EVT has also been explored in isolated PCAo. There are no randomised trials on the topic, so the data are so far solely based on observational findings. The largest study (n=243) compared EVT to BMT for P2 or P3 occlusions and found no difference in early neurological improvement or functional outcome (9). However, it reported that patients with severe symptoms or contraindication to IVT achieved more frequently early neurological improvement after EVT and observed no marked safety concerns related to the procedure. A recent systematic review and meta-analysis of 12 studies and 679 PCAo patients detected no significant difference between EVT + BMT and BMT alone in 3-month good functional outcome, rate of symptomatic intracranial haemorrhage, or mortality (10).
All in all, the current evidence encourages the use of EVT for acute stroke patients with BAo and is likely to shape treatment practices despite remaining uncertainties. When it comes to isolated PCAo, more data on efficacy and safety might be provided in the future by ongoing trials on EVT for medium vessel occlusions (e.g. NCT05029414, NCT05151172 in clinicaltrials.gov).
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